Method for removal of acetol from phenol

ABSTRACT

A method is provided for the efficient, low cost removal of acetol from a phenol stream. The method results in removal of substantially all of the acetol from the phenol stream without the formation of substantial amounts of additional methylbenzofuran. The method also avoids the use of expensive reagents and capital intensive distillation equipment.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.10/915,723 filed on Aug. 9, 2004, and which claims priority under 35.U.S.C. § 119(e) to Provisional Patent Application Ser. No. 60/556,236,which was filed on Mar. 24, 2004.

FIELD OF THE INVENTION

The present invention relates to the field of the production of highpurity phenol. More particularly, the present invention relates to theremoval of acetol from phenol to obtain desired high purity.

BACKGROUND OF THE INVENTION

The process commonly practiced for the production of phenol involves theoxidation of cumene to cumene hydroperoxide, followed by its acidcatalyzed decomposition to phenol and acetone. Isolation of phenol fromthe reaction product involves the neutralization of the acid catalyst,followed by a series of distillation and separation steps. The lowerboiling components such as acetone, unreacted cumene as well asα-methylstyrene (AMS) are first recovered from the crude product bydistillation. The remaining material is introduced into a phenolrecovery column in which phenol is distilled away from the higherboiling impurities. Depending on the distillation procedures used torecover acetone, cumene and AMS, the distilled phenol may contain minorquantities of impurities such as mesityl oxide (MO), acetol(hydroxyacetone) and other aliphatic carbonyl compounds, olefiniccompounds, acetophenone, cumylphenols and 2- and 3-methylbenzofuran(MBF) in addition to residual amounts of acetone, cumene and AMS. Suchimpurities are undesirable in phenol used in certain applications suchas in the manufacture of bisphenol-A.

MBF is a particularly undesirable contaminant of phenol that is used forcertain applications such as in the production of bisphenol-A, aprecursor to polycarbonate resins. Due to similar volatility, MBF cannotbe separated from phenol by fractional distillation. U.S. Pat. Nos.5,064,507 and 4,857,151 describe a process of distillation in thepresence of water (also called steam stripping) to reduce MBF in phenol.However, due to the high energy costs and the necessity to use largedistillation columns, this process is expensive in terms of capitalinvestment and operating costs. U.S. Pat. No. 5,414,154 describes theuse of a strong acid ion exchange resin to reduce the level of MBF byconverting it to higher boiling compounds. U.S. Pat. No. 5,414,154 alsoshowed that the effectiveness of MBF removal by resin treatmentincreases with an increase in temperature.

Although strong acid ion exchange resins also remove carbonyl compoundsfrom phenol on contact, acetol reacts with phenol to produce more MBF.U.S. Pat. No. 5,414,154 teaches the necessity to remove acetol fromphenol (e.g. by treatment with an amine) prior to contact with the resinto remove MBF.

Although effective, amine treatment involves the use of an expensivereagent, which must subsequently be purged from the phenol stream.

Both U.S. Pat. Nos. 3,810,946 and 6,489,519 disclose treatment of aphenol stream containing acetol with an acid or acid resin to removeacetol. British Patent 0 865 677 discloses a process for removing acetolfrom a phenol stream wherein the phenol stream is heated in the presenceor absence of a catalyst. However, in all of these patents, acetol isremoved by reacting it with phenol to form MBF, which is subsequentlypurged from the phenol stream.

European Patent 0 004 168 and U.S. Pat. No. 4,857,151 disclosedistillation processes to remove acetol from phenol streams. However,these methods involve the use of capital intensive distillationapparatus.

There remains a need for an efficient, low cost method for the removalof acetol from a phenol stream that does not adversely affect phenolyields by formation of significant amount of additional MBF.

SUMMARY OF THE INVENTION

The present invention provides efficient, low cost methodologies for theremoval of acetol from a phenol stream.

In one embodiment of the present invention, a method for the efficient,low cost removal of acetol from phenol comprises contacting a phenolstream containing acetol with an acidic resin at a temperature of about85° C. or less to convert acetol into higher boiling compounds otherthan methylbenzofuran. The phenol stream is then distilled to separatephenol from the higher boiling compounds.

In another embodiment of the present invention, a method for theefficient, low cost removal of acetol from phenol comprises of heatingthe phenol stream at a temperature greater than about 175° C. to convertacetol into higher boiling compounds other than methylbenzofuran. Thismay be carried out with or without added alkali metal hydroxide. Thephenol stream is then distilled to separate phenol from the higherboiling compounds.

In both embodiments of the present invention, acetol is effectivelyremoved without reacting a large portion of the acetol with phenol, thusthe present method results in reduced MBF formation and improved phenolyields.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—Illustrates the removal of acetol from a phenol stream byreaction with an acidic resin at 83° C.

FIG. 2—Illustrates the removal of acetol from a phenol stream byreaction with an acidic resin at 85° C. and the absence of the formationof significant amounts of MBF on standing at 85° C.

FIG. 3—Illustrates the formation of MBF that occurs when a phenol streamtreated with acidic resin at 85° C. is contacted directly with an acidicresin at 133° C.

FIG. 4—Illustrates the efficient removal of MBF from a phenol stream byreaction with an acidic resin at 134° C. after acetol has been removedby a low temperature treatment with acid resin followed by distillation.

FIG. 5—Illustrates the removal of acetol from a phenol stream by heatingin a closed system at 198° C.

FIG. 6—Illustrates the removal of acetol from a phenol stream by heatingin a closed system at 198° C. in the presence of 266 ppm of 50% caustic.

DESCRIPTION OF THE INVENTION

It has been discovered that acetol can be removed efficiently fromphenol at a low cost while minimizing the formation of methylbenzofuran(MBF). The treatment to remove acetol involves a treatment of distilledphenol containing acetol with either an acidic resin at low temperatureor at elevated temperature, optionally with a small amount of caustic.By this treatment, acetol present in the crude phenol is convertedprimarily to high boiling products other than MBF. These high boilingproducts can then be separated from phenol via distillation.

The removal of acetol is key to the subsequent efficient removal of MBFfrom the crude phenol. As is known, at the high temperatures and acidicconditions used to convert MBF to products separable from phenol, acetolreacts with phenol to produce more MBF. This reaction has the dualeffect of reducing phenol recovery and making the removal of MBF fromthe product less efficient.

In one embodiment of the invention, a distilled phenol stream containingacetol is contacted with an acidic resin at a temperature of about 85°C. or less to convert acetol to higher boiling compounds other than MBF.Following the acidic resin treatment, phenol is separated from thehigher boiling compounds by distillation. Treatment time and temperaturewill vary based on the quantity of acetol to be removed from the crudephenol. Treatment times can vary from 5 minutes to 1 hour. In anexemplary treatment 700 ppm of acetol was removed from a crude phenolstream by contacting with an acidic resin at a temperature of about 85°C. for about 15 minutes. Only about 12% of the acetol in this examplewas converted into MBF.

It is preferred that the acidic resin be in the form of a fixed bed,over which the phenol stream is passed. The phenol stream is preferablypassed over the resin bed at a rate of from 1 to 12 bed volumes perhour.

FIG. 1 shows the rapid reduction of acetol in a sample of phenol fromabout 225 ppm by weight to near 0 ppm on treatment with Amberlyst 36 at83° C. Note that the formation of MBF is minimal. If all of the acetolwere to be converted to MBF, a total concentration of about 400 ppm byweight of MBF would be expected. Instead, the combined concentration of2-MBF and 3-MBF is only about 25 ppm by weight. FIG. 2 again shows thetreatment of a crude phenol stream containing about 225 ppm by weight ofacetol at 85° C. with Amberlyst 36. Again, the reduction in acetolcontent to near 0 ppm is extremely rapid, with a minimal formation ofMBF. As can further be seen in FIG. 2, the extended hold time at 85° C.does not result in an increase in the content of MBF. This indicatesthat the heavy products produced from acetol by the acid resin treatmentare stable at that temperature.

The distillation following the acid resin treatment is preferably aflash distillation performed at reduced pressure to avoid the formationof MBF that would result from the breakdown of high molecular weightspecies formed during the acid treatment. The use of a flashdistillation under vacuum has the added advantage of eliminating costlydistillation apparatus used to separate phenol and acetol in prior artmethods. It will be recognized however, that various distillationmethods can be used in conjunction with the invention as long as care istaken to avoid decomposition of the high molecular weight species formedduring the acid treatment.

Referring to FIG. 3, the necessity of avoiding the decomposition of theheavy products formed during the acid resin treatment is illustrated.FIG. 3 shows the effect of a high temperature resin treatment on aphenol stream that has been treated by acidic resin at 85° C. to convertacetol to higher boil products. As can be seen, the elevated temperatureresulted in the formation of additional MBF. This indicates that thehigher boiling compounds formed in the low temperature acidic resintreatment are decomposing back to acetol at high temperature in thepresence of the acidic resin, and then reacting with phenol to form MBF.Not only does this result in a loss of phenol, but as can be seen, thetime necessary to reduce the MBF content to near 0 ppm by weight isextended significantly, approximately 130 minutes.

FIG. 4 illustrates an example where the higher boiling compounds formedby treatment with acidic resin are removed by flash distillation of thephenol prior to acidic resin treatment at elevated temperature to removeMBF. As can be seen in FIG. 4, no increase in MBF content isexperienced. Further, the MBF content is reduced to near 0 ppm in about10 minutes, as opposed to 130 minutes.

In an alternative embodiment of the invention, a distilled phenol streamcontaining acetol is heated in a closed system at elevated temperatureto convert acetol to higher boiling compounds other than MBF. The heattreatment may be carried out with or without the addition of a smallamount of caustic. If the heat treatment is carried out without theaddition of caustic, the pH of the phenol stream should be above 2,preferably above 2.5. In general, this is the pH of the distilled phenolstream from the neutralized reaction product. Lower pH may lead toadditional amounts of MBF. The caustic is preferably added as aconcentrated solution, e.g. 50 percent by weight. Again, the phenol isseparated from the higher boiling compounds via distillation. Thetemperatures used for the heat treatment will be at least 175 to 225° C.The treatment time, temperature and the amount of caustic used (ifrequired) will vary based on the quantity of acetol to be removed fromthe phenol stream. As illustrated in FIG. 5, in an exemplary treatment1036 ppm of acetol was reduced to less than 10 ppm by heating at 198° C.for about 4 hours without the addition of any caustic. In this exampleonly 1 percent of the acetol was converted into MBF. As illustrated inFIG. 6, in the presence of 266 ppm of 50% caustic, 1045 ppm of acetolwas reduced to less than 10 ppm in only about 2 hours. However, aslightly higher amount of acetol (˜1.6%) was converted into MBF. Itshould be pointed out that the efficient removal of acetol at elevatedtemperatures requires a low water content in the phenol stream beingtreated, for example less than 1.5 percent based on phenol. Preferably,the water content is reduced to about 0.1 percent by weight. Variousmethods for reducing the water content of organic streams, and phenol inparticular, are known in the art. Other examples reducing acetol from1800 ppm are shown in Table 1 below.

TABLE 1 Acetol Removal By Heat Treatment With Added Caustic 1800 ppmAcetol to 10 ppm 50% Caustic Concentration Temperature 260 ppm 525 ppm1100 ppm 175° C.   >7 hr 190° C.     5 hr   5 hr 198° C.   4.5 hr 3.5 hr2.3 hr* *2.75 hr at 1.5% water concentration

Following the treatment to remove acetol, the phenol is distilled fromthe higher boiling compounds, and can be passed to an acidic resintreatment at elevated temperature to remove MBF, as disclosed in U.S.Pat. Nos. 5,414,154 and 6,388,144 B1, both of which are incorporatedherein by reference in their entirety.

The present method to remove acetol from phenol has the advantage ofbeing more cost efficient than prior art methods that involved the useof distillation apparatus, such as super splitter columns and prior artmethods that used expensive amines. In addition, the present method hasthe advantage of producing less MBF from the acetol being removed, thanother prior art methods, which utilized high concentrations of causticor relied on multiple high temperature treatments with acidic resins.

1. A process for removing acetol from a phenol stream, said methodcomprising: providing a first phenol stream containing acetol andmethylbenzofuran, and having a water content of 1.5 weight percent orless based on phenol, heating said phenol stream at a temperature ofgreater than about 175° C. to convert acetol into higher boilingcompounds other than methylbenzofuran, such that the acetol is convertedprimarily to compounds other than methylbenzofuran, distilling saidphenol stream to separate a second phenol stream containing saidmethylbenzofuran from said higher boiling compounds, and treating saidsecond phenol stream with an acidic resin at elevated temperature toconvert methylbenzofuran to products boiling higher than phenol.
 2. Theprocess according to claim 1, wherein an alkali metal hydroxide is addedto the first phenol stream to obtain an alkali metal concentration of600 ppm by weight or less based on phenol.
 3. The process according toclaim 2 wherein said alkali metal hydroxide is sodium hydroxide.
 4. Theprocess of claim 1, wherein the first phenol stream is heated to atemperature about 175° C. to about 225° C.
 5. The process of claim 2wherein the first phenol stream contains up to 1800 ppm acetol.
 6. Theprocess of claim 1, wherein said distillation is a flash distillation.7. The process according to claim 1, wherein said heating is carried outfor a period of about 2 to about 8 hours.
 8. The method according toclaim 2, wherein said first phenol stream containing acetol is treatedto reduce the content of water in said phenol stream to 1.5 percent byweight or less based on phenol prior to said adding of an alkali metalhydroxide.
 9. The process according to claim 8, wherein said firstphenol stream is treated to reduce the content of water to 0.1 percentby weight or less based on phenol prior to said adding of an alkalimetal hydroxide.